This is interesting, why do you think they fumbled? Is it a lack of practice/experience in presenting these ideas or is it an indicator of a grad student who has become a foot soldier for a PI?
If anything, I've seen people that look great on paper, coming from the pedigreed lab/ and fancy PhD institution fail at this stage. So perhaps there's some overconfidence there. Indeed, no one in our department had any connection to, or prior knowledge of, the candidate who was ultimately given the offer. Once they got past the initial screening, through both virtual and in-person interviews, their technical depth and breadth, teaching skills and overall collegiality shone through.
All that being said, I don't doubt that all the questionable things mentioned in the article above occur, and perhaps widely. But, there is hope! And there's no better place to start than those of us who are younger faculty.